α-Synuclein (α-syn) oligomers are considered major molecules responsible for the onset of Parkinson's disease and dementia with Lewy bodies. α-Syn oligomers thus serve as an important target for the development of drugs and diagnostic tests for neurodegenerative diseases. In this paper we report on the identification of DNA aptamers that bind to soluble α-syn oligomers. A competitive screening method based on aptamer blotting was used for the selection of α-syn oligomer-specific aptamers. This approach resulted in the identification of eight aptamers that specifically bind to α-syn oligomers among α-syn monomers, oligomers, and fibrils. Interestingly, the aptamers also bound to amyloid β oligomers, which are strongly associated with the development of Alzheimer's disease. The results of this study support the hypothesis that amyloid oligomers share a common structure. Oligomer-binding aptamers may serve as powerful analytical tools for the design and development of drugs and diagnostic tests for neurodegenerative diseases.

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Alpha-synuclein is a native, unfolded protein that causes several neurodegenerative diseases such as dementia with Lewy bodies and Parkinson's disease. We have now identified the first DNA aptamers against alpha-synuclein using native PAGE applied to the SELEX method. We call this aptamer "M5-15"; it is the alpha-synuclein-bound aptamer and was isolated after four cycles of screening. M5-15 is composed of three stem-loop structures that may play an important role in the binding to alpha-synuclein. Moreover, M5-15 specifically binds to the alpha-synuclein monomer and oligomer. We expect that this aptamer will become a useful tool in alpha-synuclein analysis and diagnosis.

G-quadruplex (G4) is a DNA/RNA conformation that consists of two or more G-tetrads resulting from four-guanine bases connected by Hoogsteen-type hydrogen bonds, which is often found in the telomeres of chromatin, as well as in the promoter regions of genes. The function of G4 in the genomic DNA is being elucidated and some G4-protein interactions have been reported; these are believed to play a role in vital cellular functions. In this study, we focused on CpG methylation, a well-known epigenetic modification of the genomic DNA, especially found in the promoter regions. Although many G4-forming sequences within the genomic DNA harbor CpG sites, the relationship between CpG methylation and the binding properties of associated proteins remains unclear. We demonstrated that the binding ability of vascular endothelial growth factor (VEGF) G4 DNA to VEGF165 protein was significantly decreased by CpG methylation. We identified the binding activity of G4 DNA oligonucleotides derived from gene promoter regions to SP1, a transcription factor that interacts with a G4-forming DNA and is also altered by CpG methylation. The effect of methylation on binding affinity was accompanied by changes in G4 structure and/or topology. Therefore, this study suggested that CpG methylation might be involved in protein binding to G4-forming DNA segments for purposes of transcriptional regulation.

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